Reaction formula

Reagents

Step-by-step instruction

WARNING! This experiment is dangerous! You should NOT
perform this at home. ONLY carry out this experiment, if
you are a trained chemist, and you understand local
safety and legal requirements, which are required to
perform such experiments

I am aware of legal and safety requirements needed to
conduct this experiment

Prepare solutions of NaI and HgCl2.

Put the flask with the solution of NaJ on a magnetic stirrer.

Stir it to form a vortex.

Add a small amount (about 1-2 ml) of HgCl2 to the central part of the vortex. The orange tornado will be observed.

Scientific background

When HgCl2 is added to the NaI solution a reaction between the components takes place:
HgCl2 + NaI = HhI2 (precipitate) + 2NaCl
HgI2 is highly insoluble in water. Yellow-orange particles of the precipitate formed during reaction color the solution. In the vortex the HgI2 concentration is higher than in other parts of the solution. At a distance from the central part of the flask it reacts with the excess of NaI as follows:
HgI2 + 2NaI = Na 2(HI4)
The product of this reaction is colorless and soluble. The equilibrium between soluble and insoluble products of the reactions is the reason why on a macroscopic level something resembling a tornado is observed.

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